The Green Challenge: CO2 meets H20.

Water Works

CO2 meets H2O.

Think water and global warming, and melting Arctic ice caps may come to mind—a problem that can seem pretty insurmountable. But the water in your sink and dishwasher and bathtub also has a CO 2 cost associated with global warming. And it is a cost you can reduce. Using less water means less waste and pollution. Using less hot water means fewer CO 2 emissions. The average American household expends about 14 percent of its energy usage on heating water, according to the Natural Resources Defense Council. That adds up to nearly 4 percent of the country's total energy use and spins off about 260 million tons of carbon dioxide emissions.

A lot of excess water simply goes down the drain. Then there are gushy toilets and showers. According to the Rocky Mountain Institute, Americans with inefficient fixtures and appliances use about 80 gallons of water per person per day inside their homes. Replacing old and conventional faucets, washing machines, toilets, and showers with energy-efficient and low-flow varieties can stanch the flow by as much as a third—and you'll also trim CO2 emissions. How you heat up water makes a difference, too. Our suggestions for washing away your CO2 sins:

• If you have an old or conventional shower head, switch to a low-flow version and save gallons of water a day. (Learn here how to check the flow rate of your existing shower head and replace it with a low-flow one.) Some low-flows deliver excellent water pressure with only 1 to 2.2 gallons per minute (as opposed to the current government standard of 2.5 gallons per minute or pre-1992 shower heads that use even more water). Aerating, low-flow shower heads mix air into the water stream to maintain steady water pressure. Nonaerating shower heads deliver a stronger spray and tend to pulse. Both types of fixtures can cost as little as $20; the money you'll save on your energy, water, and sewer bills will likely repay your investment in less than a year. Check out some TreeHugger-recommended brands here.

• A bathroom-sink faucet need deliver only 0.5 to 1 gallon of water per minute. In the kitchen, you want 2 or 2.5 gallons per minute so you won't get frustrated when you're filling pots. If your faucets are higher pressure and ready to be replaced, pick a lower-pressure model.

• Showers account for two-thirds of all water heating costs. The shorter your shower time, the more CO2 you'll save.

• Take showers instead of baths, which use more water.

• Turn the water off while you shave.

• Unless your dishes are really dirty, scrape instead of rinsing them before loading them into the dishwasher, especially if your dishwasher automatically prerinses or has a rinse-hold cycle. Also, use the energy-saver option, let the dishes air-dry, and, if possible, choose the light or cold-wash option. And wait until the dishwasher is full to run it.

• Which is more efficient—you or the dishwasher? Machine bests man in this debate: Hand-washing uses an average of 10 to 15 gallons of water, while automatic dishwashers use about 8. If you don't own a dishwasher or need to wash pots by hand, don't let water run while you're scrubbing.

• Instead of using hot water to thaw frozen food, let it defrost on the counter or in the refrigerator.

• An old water heater can operate for years at very low efficiency before it completely breaks down. If yours is more than 10 years old, it's likely running at less than 50 percent efficiency. Replace it with an energy-efficient one or, better yet, a heater without a tank, which warms up water only as you need it rather than holding hot water at the ready all the time. (Learn how to calculate how much hot water your household uses at peak times here. Learn more about water heaters here.)

• Insulating your hot-water heater is a cheap and easy way to make it more efficient. Most hardware stores carry water-heater blankets, which cost about $10 to $20 and can reduce heat loss by 25 percent to 45 percent. (Here's how to buy and install one.)

• If you have a choice between using appliances run on natural gas or run on electricity, choose natural gas, which is generally cleaner in terms of CO2 emissions and also costs less.

• Solar water-heating systems can be used in any climate to heat your water supply. Since they use no fossil fuel energy, they save a lot of CO2 emissions. A typical household can meet 50 percent to 80 percent of its hot water needs using solar heat. Though they cost slightly more to install than a traditional system, your fuel source—the sun—is free. (Learn the basics on solar water-heating systems here. For more details, click here.)

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